This invention relates to an optical printing system capable of printing characters, patterns or the like by using light.
Printers utilized in computers or the like are classified into various types according to their printing systems. Use of photoprinters has been increased in recent years because of their high printing speed and low operating noise. As the apparatus of this type, those utilizing electrophotographic technique are used in most cases. According to the electrophotographic technique, an image of a character or a pattern is formed on a charged photosensetive member by utilizing a suitable optical system, powders of colored resin called toner is adhered to the not-irradiated portion on the photosensitive member that is the portion still retaining charge, the adhered powders are transferred onto a copying paper, and then the transferred powder image is fixed to obtain a copy.
The photoprinter described above requires to use a photoconductor, a toner applying apparatus and a heat fixing device of the toner. Moreover, as the toner is a consumptive material it is necessary to always store and supplement the toner. For this reason, the construction of the apparatus becomes complicated and the maintenance thereof is troublesome.
There has also been used a photocolor printer in which colored characters or picture images are printed on a photo and pressure sensitive sheet by photo-signals such as laser photo-signals.
A laser printer of a well known construction is illustrated in FIG. 7. As shown, the laser printer comprises a laser beam oscillator 301, a modulator 302, a polygonal scanning mirror 303, a f.theta. lens 305, a photosensitive drum 306 including charging device 307, a toner developing device 308, a transferring device 309 and a charge removing and cleaning device 310. A recording paper 311 is passed between the photosensitive drum 306 and the transferring device 309 and guided to the fixing device 312. In this printer, the laser beam emitted by the laser beam oscillator 301 is turned ON and OFF by the modulator 302 in accordance with character or picture image informations outputted from a control unit contained in the printer. The photo-signals thus formed are projected upon the photosensitive drum 306 through the scanning mirror 303 and the f.theta. lens 305 so as to form an electrostatic latent image on the photosensitive drum 306 corresponding to the outputted informations. Then, the toner is caused to adhere to the electrostatic latent image on the drum 306 and the resulting toner image is transferred onto the recording paper 311 and then fixed by the fixing device 312. In this prior art laser printer, character or picture images of only a single color can be recorded. An ordinary paper is used as the copying paper and the toner is caused to adhere onto the paper to print the character or the picture images. Consequently, resolution is low and the photosensitive drum and other accessories complicate the construction of the printer.
In a color printer other than the laser printer described above multicolor toners (for example, red, green and blue colors) or color ink ribbons are used to obtain a print of all colors. With such color printing system, however, as it is necessary to print the same portion of the recording paper by the times the same as the number of colors. Accordingly, the printing speed becomes low.